Quinoxaline-containing hyperbranched poly(benzoxazoles) rights of the government

ABSTRACT

A hyperbranched polymer having repeating units of the formula:                    
     wherein Q is —O—, —S— or —NH—.

RIGHTS OF THE GOVERNMENT

The invention described herein may be manufactured and used by or forthe Government of the United States for all governmental purposeswithout the payment of any royalty.

BACKGROUND OF THE INVENTION

The present invention relates to a new quinoxaline-containinghyperbranched polymers.

Dendritic macromolecules such as dendrimers and hyperbranched polymersare a new class of highly branched polymers that have distinctlydifferent properties from their linear analogs. Both dendrimers andhyperbranched polymers have much lower solution and melt viscositiesthan their linear analogs of similar molecular weights. They also have alarge number of chain-ends whose collective influence dictates theiroverall physical and/or chemical behaviors. These features areattractive in terms of processability and offering flexibility inengineering required properties for specific applications. However,there is a practical advantage that hyperbranched polymers have overdendrimers at “raw material” level. Although dendrimers have preciselycontrolled structures (designated as generations), their preparationsgenerally involve tedious, multi-step sequences that are impractical andcostly in scale-up production. Synthesis of a hyperbranched polymer, onthe other hand, is a one-pot process. Large quantities of hyperbranchedpolymers can be easily produced from AB_(x) (x≧2) monomers.

Because of their excellent thermal and mechanical properties, as well astheir optical and electronic characteristics, aromatic, fusedheterocyclic polymers such as polyquinoxalines and polybenzoxazolescontinue to attract considerable attention. However, they have limitedprocessability due to the nature of fused ring systems. Theirinsolubility and their softening temperatures are generally above theirdegradation temperatures. Chemical modification on the these materials,for example, by the use of solubilizing pendants or flexible units inthe main chain, has been successful to improve their processability,allowing the optimization of their properties as a function ofprocessability. Another viable approach to achieving this objective isto incorporate the elements of local rigidity and global randomness intothe macromolecular architecture. Local rigidity provides the thermal,electronic and optical characteristics of the aromatic fused systemswhile global randomness frustrates entanglement of the polymer chains,leading to greater solubility. Dendritic structures clearly embody thesequalities. However, as noted previously, hyperbranched structures havegreater synthetic practicality.

Accordingly, it is an object of the present invention to provide novelquinoxaline-containing hyperbranched benzazole polymers.

Other objects and advantages of the invention will be set forth in partin the description which follows, and in part will be obvious from thedescription, or may be learned by practice of the invention. The objectsand advantages of the invention may be realized and attained by means ofthe instrumentalities and combinations particularly pointed out in theappended claims.

SUMMARY OF THE INVENTION

In accordance with the present invention there are providedquinoxaline-containing hyperbranched benzazole polymers having repeatingunits of the formula:

wherein Q is —O—, —S— or —NH—.

The polymer of this invention can be endcapped with a variety of unitsincluding, but not limited to, —OH,

DETAILED DESCRIPTION OF THE INVENTION

The quinoxaline-containing hyperbranched benzazole polymers of thisinvention are prepared by polymerization of the corresponding AB₂monomer

wherein Z is —OH, —SH or —NH₂HCl.

Briefly, the AB₂ monomer,2,3-bis(3-amino-4-hydroxyphenyl)quinoxaline-6-carboxylic aciddihydrochloride, is synthesized by condensing 3,4-diaminobenzoic acidand 4,4′-dimethoxybenzil to afford 2,3-bis(4-methoxyphenyl)quinoxaline-6-carboxylic acid, followed by demethylation in hydrobromicacid in acetic acid to form 2,3-bis(4-hydroxyphenyl)quinoxaline-6-carboxylic acid. The latter is then nitrated using nitricacid (70% conc.) in acetic acid at room temperature, yielding2,3-bis(3-nitro-4-hydroxyphenyl) quinoxaline-6-carboxylic acid. Thedesired monomer is prepared by catalytic reduction in the presence ofpalladium catalyst in 10% hydrochloric acid.

The AB₂ monomer, 2,3-bis(3,4-diaminophenyl) quinoxaline-6-carboxylicacid dihydrochloride, is synthesized in similar fashion, starting with3,4-diaminobenzoic acid and 4,4′-dinitrobenzil. The condensation productis methylated to protect the carboxy group, reduced, acetylated toprotect the amino groups, nitrated and reduced to provide the desiredmonomer.

The AB₂ monomer, 2,3-bis(3-amino-4-mercaptophenyl)quinoxaline-6-carboxylic acid dihydrochloride, is synthesized bycondensing 3,4-diaminobenzoic acid and 3,3′-diaminobenzil. Thecondensation product is then methylated to protect the carboxylic acidgroup, subjected to catalytic hydrogenation to reduce the nitro groupsto amines, treated with thiocyanogen bromide (generated in-situ frombromine and ammonium thiocynate), and finally hydrolyzed to provide thedesired monomer.

Polymerization of the AB₂ monomer can be conducted in polyphosphoricacid (PPA) at a polymer concentration of about 6 weight percent at atemperature of about 120° to 150° C., or in the melt state.

Due to the availability of large number of end-groups, theend-functionalization of hyperbranched polymers can be utilized totailor their physical properties for various applications. The number ofreactive end-groups is equal to the degree of polymerization plus one(DP+1). The hyperbranched polymers can be endcapped using, for examplebut not limited to, 2-thiophenecarboxylic acid, 3,5-benzoic acid,3-sulfobenzoic acid, 4-sulfobenzoic acid and2,3-diphenylquinoxaline-6-carboxylic acid.

The hyperbranched polymers of this invention are suitable for use inapplications where the material will be subject to high servicetemperatures.

The following examples illustrate the invention:

EXAMPLE 1 2,3-Diphenylquinoxaline-6-carboxylic Acid

Into a 500 mL three-necked, round-bottomed flask equipped with amagnetic stirrer, a condenser, and a nitrogen inlet, 3,4-diaminobenzoicacid (16.0 g, 105 mmol) was dissolved in deoxygenated acetic acid (250mL). Benzil (21.0 g, 100 mmol) was then added in one portion. Themixture was heated under reflux for 12 h. During this time, off-whiteprecipitate formed. After the reaction mixture was allowed to cool toroom temperature, the precipitate was collected to give 32.2 g (99%yield) of crude product, m.p. 290.5-292° C. Recrystallization of thecrude product from DMF afforded 29.6 g (91% yield) of pink crystals,m.p. 291-292.5° C. Anal. Calcd. for C₂₄H₁₄N₂O₂: C, 77.29%; H, 4.32%; N,8.57%; O, 9.80%. Found: C, 76.93%; H, 4.77%; N, 8.57%; O, 9.63%. FT-IR(KBr, cm⁻¹): 1690 (carbonyl). Mass spectrum (m/e): 326 (M+, 100%relative abundance). ¹H-NMR (DMSO-d₆, δ in ppm): 7.35-7.43 (m, 6H, Ar),7.48-7.51 (d, 4H, Ar), 8.18-8.21 (d, 1H, Ar), 8.28-8.32 (dd, 1H, Ar),8.65 (s, 1H, Ar), 13.51 (s, 1H, COOH). ¹³C-NMR (DMSO-d₆, δ in ppm):128.00, 128.20, 128.95, 129.04, 129.15, 129.41, 129.67, 130.65, 132.01,138.31, 139.61, 142.23, 153.98, 154.61, 166.50.

EXAMPLE 2 2,3-Bis(4-methoxyphenyl)quinoxaline-6-carboxylic Acid

Into a 500 mL three-necked, round-bottomed flask equipped with amagnetic stirrer, a nitrogen inlet, and a condenser, 3,4-diaminobenzoicacid (14.21 g, 93.4 mmol) was dissolved in deoxygenated acetic acid (250mL). 4,4′-Dimethoxybenzil (25,0 g, 92.5 mmol) was then added to brownclear mixture at room temperature. The reaction mixture was heated underreflux with vigorous stirring for 8 h. After having been allowed to cooldown to room temperature, the brown mixture was poured into distilledwater. The resulting light brown precipitates were collected by suctionfiltration and then air-dried overnight. It was recrystallized fromethanol to give 34.8 g (97% yield) of yellow solid, m.p. 296-298° C.Anal. Calcd. for C₂₃H₁₈N₂O₄: C, 71.49%; H, 4.70%; N, 7.25%; Found: C,71.51%; H, 4.55%; N, 7.11%. FT-IR (KBr, cm⁻¹): 1693 (carbonyl), 2838(methyl). Mass spectrum (m/e): 386 (M+, 100% relative abundance). ¹H-NMR(DMSO-d₆, δ in ppm): 3.80 (s, 6H, OCH3), 6.92-6.96 (d, 4H, Ar),7.44-7.48 (dd, 4H, Ar), 8.8.11-8.14 (d,1H, Ar), 8.22-8.26 (dd,1H, Ar),8.58-8.59 (d,1H, Ar), 13.49 (s,1H, COOH). ¹³C-NMR (DMSO-d₆, δ in ppm):55.12, 113.52, 128.90, 128.98, 130.48, 130.74, 131.06, 131.17, 131.49,139.38, 142.08, 153.46, 154.06, 159.85, 159.97, 166.59.

EXAMPLE 3 2,3-Bis(4-hydroxyphenyl)quinoxaline-6-carboxylic Acid

Into a 1000 mL three-necked, round-bottomed flask equipped with amagnetic stirrer, a nitrogen inlet, and a condenser,2,3-bis(4-methoxyphenyl)-quinoxaline-6-carboxylic acid (34.7 g, 89.8mmol) was dissolved in acetic acid (260 mL). Hydrobromic acid (48%, 500mL) was then added to yellow clear mixture at room temperature. Thereaction mixture was heated under reflux with vigorous stirring untilthe solution become homogeneous. It took about 6 h. After having beenallowed to cool down to room temperature, the red-brown mixture waspoured into distilled water. The resulting light brown precipitate wascollected by suction filtration and dried under the reduced pressure togive 31.9 g (99% crude yield) of yellow solid, m.p. 315-317° C. (dec.).Anal. Calcd. for C₂₁H₁₄N₂O₄: C, 70.39%; H, 3.94%; N, 7.82%. Found: C,66.70%; H, 3.98%; N, 7.20%. FT-IR (KBr, cm⁻¹): 1698 (carbonyl), 3396(hydroxy). Mass spectrum (m/e): 358 (M+, 100% relative abundance).¹H-NMR (DMSO-d₆, δ in ppm): 6.76-6.79 (d, 4H, Ar), 7.35-7.39 (d, 4H,Ar), 8.09-8.12 (d, 1H, Ar), 8.20-8.24 (d, 1H, Ar), 9.87-9.89 (d, 1H,OH), 13.50 (s, 1H, COOH). ¹³C-NMR (DMSO-d₆, δ in ppm): 114.93, 128.78,129.21, 129.27, 130.39, 131.11, 131.23, 139.29, 142.06, 153.78, 154.38,158.30, 158.44, 166.62.

EXAMPLE 4 2,3-Bis(4-hydroxy-3-nitrophenyl)quinoxaline 6-carboxylic Acid

Into a 500 mL three-necked, round-bottomed flask equipped with amagnetic stirrer, a nitrogen inlet, and a dropping funnel,2,3-bis(4-hydroxyphenyl)quinoxaline-6-carboxylic acid (10.0 g, 27.9mmol) was dissolved in acetic acid (200 mL). A solution of nitric acid(5 mL) in acetic acid (20 mL) was then added dropwise at roomtemperature for 20 min. The reaction mixture was stirred for additional12 h at room temperature. The light orange mixture was poured intodistilled water. The resulting yellow precipitates were collected bysuction filtration and then air-dried overnight. Recrystallization ofthe crude product from acetic acid gave 12.2 g (97.5% yield) of brightyellow solid, m.p. 263-267.5° C. Anal. Calcd. for C₂₁H₁₂N₄O₈: C, 56.26%;H, 2.70%; N, 12.50%; O, 28.55%. Found: C, 55.99%; H, 3.06%; N, 12.14%;O, 27.68%. FT-IR (KBr, cm⁻¹): 1347, 1540 (Ar-NO₂), 1628 (carbonyl), 3421(hydroxy). Mass spectrum (m/e): 448 (M+, 100% relative abundance).¹H-NMR (DMSO-d₆, δ in ppm): 7.14-7.18 (dd, 2H, Ar), 7.61-7.65 (dd, 2H,Ar), 8.16-8.32 (m, 4H, Ar), 8.62-8.63 (d, 1H, Ar), 11.54 (s, 1H, COOH).¹³C-NMR (DMSO-d₆, δ in ppm): 118.87, 118.99, 126.82, 126.91, 128.84,128.90, 129.10, 129.59, 129.70, 130.48, 132.15, 136.18, 136.27, 136.56,139.61, 142.23, 151.65, 152,25, 152.85, 152.94, 166.45.

EXAMPLE 5 2,3-Bis(3-amino-4-hydroxyphenyl)quinoxaline-6-carboxylic AcidDihydrochloride

Into a 500 mL high pressure bottle, 2,3-bis(4-hydroxy-3-nitrophenyl)quinoxaline-6-carboxylic acid (10.0 g, 22.3 mmol), palladium onactivated carbon (10%, 0.5 g), and 10% hydrochloric acid solution (150mL) were introduced. The bottle was placed on a Parr hydrogenator,purged with hydrogen several times, and then agitated at 60-65 psi for24 h. After the resulting mixture had been filtered through Celite 545to remove catalyst, the solvent was removed by vacuum distillation. Theoff-white residue was recrystallized from deoxygenated 20 % hydrochloricacid to give 6.7 g (65% yield) of white crystals, m.p. 260° C. (dec.).Anal. Calcd. for C₂₁H₁₈Cl₂N₄O₄: C, 54.68%; H, 3.93%; Cl, 15.37%; N,12.15%; Found: C, 48.80%; H, 4.75%; Cl, 20.79%; N, 10.91%. FT—IR (KBr,cm⁻¹): 1293 (Ar—NH₂), 1628 (carboxy), 3421 (Ar—OH). Mass spectrum (m/e):344 (M+—CO₂—2HCI 100% relative abundance). ¹H-NMR (DMSO-d₆, δ in ppm):7.13-7.16 (d, 2H, Ar), 7.30-7.31 (d, 2H, Ar), 7.78 (s, 2H, Ar),8.17-8.21 (d, 1H, Ar), 8.27-8.28 (d, 2H, Ar), 8.6-8.61 (s, 1H, Ar),10.11 (s, 4H, NH2), 11.47 (s, 2H, —OH). ¹³C-NMR (DMSO-d₆, δ in ppm):115.79, 118.99, 125.61, 128.95, 129.07, 129.13, 129.33, 130.36, 130.80,131.83, 139.41, 142.08, 152.13, 152.51, 153.08, 166.42.

EXAMPLE 6 Hyperbranched poly(quinoxaline-benzoxazole) with o-aminophenolEndgroups

Into a 100 mL resin flask equipped with a high torque mechanicalstirrer, nitrogen inlet and outlet, and a pressure regulator,polyphosphoric acid (PPA, 30 g) was placed and stirred with driednitrogen purging for 10 h. The monomer, 2,3-bis(3-amino-4-hydroxyphenyl)6-quinoxaline-carboxylic acid dihydrochloride (3.0 g, 6.5 mmol) wasadded and the resulting mixture was dehydrochlorinated under reducedpressure (1 mmHg) at 60° C. for 24 h and 100° C. for 6 h. Uponcompletion of the dehydrochlorination process, the mixture was gentlyheated to 130° C. When the oil-bath temperature was close to 130° C.,the mixture was already too viscous to render further stirringineffective. All the polymer dope was stuck onto the glass-rod stirrerand therefore, it was allowed to stand for 30 min at 130° C. At the endof the polymerization process, water was added into the flask and theresulting mixture was poured into a Waring blender. The polymericproduct that initially formed bundles with residual PPA was chopped inthe blender, collected by suction filtration, washed with dilutedammonium hydroxide and then repeatedly with large amounts of water.Finally, the hyperbranched polymer was dried under reduced pressure (1mmHg) at 200° C. for 48 h. Its intrinsic viscosity was determined to be1.04 dL/g (MSA, 30±0.1° C.). Anal. Calcd. for C₂₁H₁₂N₄O₂: C, 71.58%; H,3.43%; N, 15.90%. Found: C, 69.56%; H, 3.68%; N, 15.17%. Thehyperbranched polymer is designated as PPQO-5 in Table I, below.

EXAMPLE 7 General Procedure for in-situ End-Capping Reaction (Method 1)

Into a 100 mL resin flask equipped with a high torque mechanicalstirrer, a nitrogen inlet and outlet, and a pressure regulator, PPA (30g) was placed and stirred with dried nitrogen purging for 10 h. Theend-capper (90 mol% to AB₂ monomer) was added and heated to 100° C.until the mixture became homogeneous (2 h). The monomer,2,3-Bis(3-amino-4-hydroxyphenyl) quinoxaline-6-carboxylic aciddihydrochloride (3.0 g, 6.5 mmol) was added and the resulting mixturewas dehydrochlorinated under reduced pressure (1 mmHg) at 60° C. for 24h and 100° C. for 6 h. Upon completion of the dehydrochlorination, themixture was gently heated to 130° C. for 24 h, and 160° C. for 24 h. Thework up was followed as described in the previous procedure. The powderyproduct was finally dried under reduced pressure (1 mmHg) at 200° C. for48 h. A range of intrinsic viscosities of 0.18-0.22 dL/g (MSA, 30±0.1°C.) were determined.

EXAMPLE 8 General Procedure for “Post-Polymerization” End-Capping(Method 2)

Into a 100 mL resin flask equipped with a high torque mechanicalstirrer, a nitrogen inlet and outlet, and a pressure regulator, PPA (10g) was placed and stirred with dried nitrogen purging for 10 h. Theparent hyperbranched polymer from Example 6 (1.0 g, 2.8 mmol, [η]=1.04dL/g) was added and stirred at 100° C. until the mixture becomehomogeneous. It usually took about 2-4 h. The corresponding endcapper(3-sulfobenzoic acid 5% excess amount), was then added at thistemperature and stirred for 24 h, then at 160° C. for 48 h. The work upwas followed as mentioned in the previous procedure. The powdery productfinally dried under reduced pressure (1 mmHg) at 200° C. for 48 h. Anintrinsic viscosity of 0.35 dL/g (MSA, 30±0.1° C.) was determined: Anal.Calcd. for C₂₈H₁₄N₄O₅S: C, 64.86%; H, 2.72%; N, 10.81%, 15.43%, 6.18%.Found: C, 63.36%; H, 3.43%; N, 10.42%, 13.97%. 5.33%.

EXAMPLE 9 Specific Endcapped Polymers

PPQO-6 was prepared by the reaction of 2,3-Bis(3-amino-4-hydroxyphenyl)quinoxaline-6-carboxylic acid dihydrochloride (Example 5), hereinafterreferred to as AB₂ monomer, and monocarboxyl end-capper2,3-diphenyl-6-carboxyquinoxaline (method 1). PPQO-7 was prepared by thereaction of AB₂ monomer and 4-sulfobenzoic acid (method 1). PPQO-8 wasprepared by the reaction of AB₂ monomer and 3-sulfobenzoic acid (method2). Two attempts were made to prepare PPQO-9. The attempt to reactPPQO-5 and 2-thiophenecarbonyl chloride (method 2) resulted in theformation of insoluble gel. Soluble PPQO-9 was prepared by the reactionof AB₂ monomer and 2-thiophenecarboxylic acid (method 1) at milderreaction conditions. PPQO-10 was prepared by the reaction of AB₂ monomerand 3,5-dihydroxybenzoic acid (method 1). The viscosity value andthermal properties of PPQO's 5-10 are given in Table I, below.

TABLE I T_(5%) (° C.)^(d) In η* In Air Char (%) Helium Char (%) PPQO-Method (dL/g)^(a) T_(g) (° C.)^(b) (Onset) at 900° C. (Onset) at 900° C.5 — 1.04^(e)  ND^(c) 421 0.5 480 50 (533) (619) 6 1 0.19 ND — — — — 7 10.18 ND — — — — 8 2 0.35^(e) ND  296^(f) 2  288^(f) 23 (510) (624) 9 10.22 ND — — — — 9 2 Insol. ND — — — — 10  1 0.23 ND 297 3 301 55 (486)(580) Note: ^((a))Reduced viscosity determined with 0.5% solution in MSAat 30 ± 0.1° C. ^((b))Glass transition temperature (T_(g)) determined byDSC with heating rate of 10° C./min ^((c))ND = not detectable up to 450°C. ^((d))The temperature at which 5% weight loss based on TGA thermogramobtained with a heating rate of 10° C./min ^((e))Intrinsic viscositydetermined by two points extrapolation to the origin in MSA at 30 ± 0.1°C. ^((f))Desulfonylation temperature

Having thus described exemplary embodiments of the present invention, itshould be noted by those skilled in the art that the disclosures hereinare exemplary only and that alternatives, adaptations and modificationsmay be made within the scope of the present invention.

We claim:
 1. A hyperbranched polymer having repeating units of theformula:

wherein Q is —O—, —S— or —NH—.
 2. The polymer of claim 1 wherein Q is—O—.
 3. The polymer of claim 2, endcapped with —OH.
 4. The polymer ofclaim 2, endcapped with


5. The polymer of claim 2, endcapped with


6. The polymer of claim 2, endcapped with


7. The polymer of claim 2, endcapped with